In terms of geographical size, Northeast India constitute about 8% of the total India's size, and is roughly 3/4th the size of the state of Maharashtra. Northeast India's population (all 8 states combined) is approximately 40 million (2011 census), which represents 3.1% of the total Indian population (1,210 million). Northeast India's population size is roughly equal to the state of Odisha.

The Siliguri Corridor in West Bengal, with a width of 21 to 40 kilometres (13 to 25 mi),[1] connects the North Eastern region with the main part of India. The region shares more than 4,500 kilometres (2,800 mi) of international border (about 90 per cent of its entire border area) with China (South Tibet) in the north, Myanmar in the east, Bangladesh in the southwest, and Bhutan to the northwest.[1]

The earliest settlers were Austro-Asiatic speakers,[5] followed by Tibeto-Burmese[6] and then by Indo-Aryans.[7] Due to the bio- and crop diversity of the region the focus of current archaeological research has been on domestication of several important plants by early settlers.[8] Writers have suspected an early trade route via Northeast India in the references of Chinese explorer, Zhang Qian made in 100 BC.[9] The Periplus of the Erythraean Sea mention a people called Sêsatai in the region,[10] who were the source of malabathron, so prized in the old world.[11]

In the early historical period (most of first millennium), Kamarupa straddled most of present-day Northeast India, besides Bhutan and Sylhet in Bangladesh. Xuanzang, the traveling Chinese monk, visited Kamarupa in the 7th century, and described the people as "short in stature and black-looking", whose speech differed a little from mid-India and who were of simple but violent disposition; and that the people in Kamarupa knew of Sichuan that lay to the kingdom's east beyond a treacherous mountain.[12]

Established during the British Raj, the northeastern states were isolated from their traditional trading partners such as Bhutan and Myanmar.[13]

The city of Shillong acted as the capital of the Assam province created during the British Rule. It remained as the capital of undivided Assam until formation of the state of Meghalaya in 1972.[17] The capital of Assam was then shifted to Dispur, a part of Guwahati, and Shillong became the capital of Meghalaya.

in 1944, the Japanese planned a daring attack on India. Traveling through Burma, it was stopped at Kohima and Imphal by British and Indian troops. This marked the furthest western expansion of the Japanese Empire and presaged Allied victory.

In 1947 Indian independence and partition resulted in a landlocked region, exacerbating the isolation that has been recognized, but not studied. Muslim Bangladesh controlled access to the Indian Ocean.[19] The mountainous terrain has hampered the road and railways connection in the region.[citation needed]

The Northeast region can be physiographically categorised into the Eastern Himalayas, Northeast Hills (Patkai-Naga Hills and Lushai Hills) and the Brahmaputra and the Barak Valley Plains. Northeast India (at the confluence of Indo-Malayan, Indo-Chinese, and Indian biogeographical realms) has a predominantly humid sub-tropical climate with hot, humid summers, severe monsoons and mild winters. Along with the west coast of India, this region has some of the Indian sub-continent's last remaining rain forests which supports diverse flora and fauna and several crop species. Similarly, reserves of petroleum and natural gas in the region constitute a fifth of India's total potential. The region is covered by the mighty Brahmaputra-Barak river systems and their tributaries. Geographically, apart from the Brahmaputra, Barak and Imphal valleys and some flat lands in between the hills of Meghalaya and Tripura, the remaining two-thirds of the area is hilly terrain interspersed with valleys and plains; the altitude varies from almost sea-level to over 7,000 metres (23,000 ft) above MSL. The region's high rainfall averaging around 10,000 millimetres (390 in) and above creates problems of ecosystem, high seismic activity and floods. The states of Arunachal Pradesh and Sikkim have a montane climate with cold, snowy winters and mild summers.

WWF has identified the entire Eastern Himalayas as a priority Global 200 Ecoregion while Conservation International has upscaled the Eastern Himalaya Hotspot which initially covered the states of Arunachal Pradesh, Sikkim, Darjeeling Hills, Bhutan, and Southern China to the Indo Burma (Hotspot) which now includes all the eight states of North-East India, along with the neighbouring countries of Bhutan, southern China and Myanmar. The population and diversity of the region’s birds largely reflects the diversity of habitats associated with a wide altitudinal range. North East India supports some of the highest bird diversities in the orient with about 850 bird species. The Eastern Himalaya and the Assam plains have been identified as an Endemic Bird Area by the Royal Society for Protection of Birds, (ICBP 1992). The global distribution of 24 restricted-range species is limited to the region. The region’s lowland and montane moist-to-wet tropical evergreen forests are considered to be the northernmost limit of true tropical rainforests in the world.[26]

The region has been identified by the Indian Council of Agricultural Research as a centre of rice germplasm while the National Bureau of Plant Genetic Resources (NBPGR), India, has highlighted the region as being rich in wild relatives of crop plants. It is the centre of origin of citrus fruits. Two primitive variety of maize, Sikkim Primitive 1 and 2 have been reported from Sikkim (Dhawan, 1964). Although jhum cultivation, a traditional system of agriculture, is often cited as a reason for the loss of forest cover of the region, this primary agricultural economic activity practised by local tribes reflects the usage of 35 varieties of crops. The region is rich in medicinal plants and many other rare and endangered taxa. Its high endemism in both higher plants, vertebrates and avian diversity has qualified it to be a biodiversity ‘hotspot’ and this aspect has been elaborated in details in the subsequent sections. In 1995, International Union for Conservation of Nature identified Namdapha in Arunachal Pradesh as a centre of plant diversity.[citation needed]

The following figures highlight the biodiversity significance of the region:[27]

Out of the nine important vegetation types of India, six are found in the North Eastern region.

These forests harbour 8,000 out of 15,000 species of flowering plants. In floral species richness, the highest diversity is reported from the states of Arunachal Pradesh (5000 species) and Sikkim (4500 species) amongst the North Eastern States.

According to the Indian Red data book published by the Botanical Survey of India, 10 percent of the flowering plants in the country are endangered. Of the 1500 endangered floral species, 800 are reported from North East India.

Most of the North Eastern states have more than 60% of their area under forest cover, a minimum suggested coverage for the hill states in the country.

North East India is a part of Indo-Burma 'hotspot'. The hotspot is the world's second largest, next only to the Mediterranean basin with an area 2,206,000 square kilometres (852,000 sq mi) among the 25 identified.[citation needed]

The International Council for Bird Preservation, UK identified the Assam plains and the Eastern Himalaya as an Endemic Bird Area (EBA). The EBA has an area of 220,000 km2 following the Himalayan range in the countries of Bangladesh, Bhutan, China, Nepal, Myanmar and the Indian states of Sikkim, northern West Bengal, Arunachal Pradesh, southern Assam, Nagaland, Manipur, Meghalaya and Mizoram. Because of a southward occurrence of this mountain range in comparison to other Himalayan ranges, this region has a distinctly different climate with warmer mean temperatures and fewer days with frost and have much higher rainfall. This has resulted in the occurrence of a rich array of restricted range bird species. More than two critically endangered species, three endangered species and 14 vulnerable species of birds are in this EBA. Stattersfield et al. (1998) identified 22 restricted range species out of which 19 are confined to this region and the remaining three are present in other endemic and secondary areas. Eleven out of the 22 restricted range species found in this region are considered as threatened (Birdlife International 2001), a number greater than in any other EBA of India.

WWF has identified the following priority ecoregions in North-East India:

Sipahijola Wildlife Sanctuary is a wildlife sanctuary in Tripura, India. It covers an area of about 18.53 square kilometres (7.15 sq mi) and is located about 25 kilometres (16 mi) from the city centre.[34] It is a woodland with an artificial lake and natural botanical and zoological gardens. The sanctuary boasts of abounding congregation of wildlife, especially birds and primates, the terrain is absolutely green throughout the year and so is the beautiful weather except for the two humid summer months of March and April. It gives shelter to about 150 species of birds and the unique bespectacled monkey (Phayre's langur).

According to 2001 census, the total literacy rate of the population in the region at 68.5 per cent, with female literacy rate at 61.5 per cent, is higher than the country's average of 64.8 per cent and 53.7 per cent respectively. There are variations in the literacy rates among different states with Assam, Arunachal Pradesh and Meghalaya below the national average while Mizoram and Tripura tops the list not only in the following region but in the entire nation.

Northeast India constitutes a single linguistic region with about 220 languages in multiple language families (Indo-European, Sino-Tibetan, Tai–Kadai, Austroasiatic)[36] that share common structural features.[37]Assamese, an Indo-Aryan language spoken mostly in the Brahmaputra Valley, developed as a lingua franca for many speech communities. Assamese-based pidgin/creoles have developed in Nagaland (Nagamese) and Arunachal (Nefamese),[38] though their use has been on a decline in recent times. The Austro-Asiatic family is represented by the Khasi, Jaintia and War languages of Meghalaya. A small number of Tai–Kadai languages (Ahom, Tai Phake, Khamti, etc.) are also spoken. Sino-Tibetan is represented by a number of languages that differ significantly from each other,[39] some of which are: Bodo, Rabha, Karbi, Mising, Tiwa, Deuri etc. (Assam); Garo, (Meghalaya) Ao, Tangkhul, Angami, Sema, Lotha, Konyak etc.(Nagaland); Mizo, Hmar,Chakma (Mizoram); Hrusso, Tanee, Nisi, Adi, Abor, Nocte, Apatani, Misimi etc. (Arunachal). Manipuri is the official language in Manipur, the dominant language of the Imphal Valley; while Naga languages such as Mao, Maram and Tangkul, and Kuki languages such as Hmar and Paite predominate in individual hill areas of the state.

Among other Indo-Aryan languages, Sylheti is spoken in South Assam in the Barak Valley. Besides the Sino-Tibetan Tripuri language, Bengali is a majority language in Tripura. Nepali, an Indo-Aryan language, is dominant in Sikkim, besides the Sino-Tibetan languages Limbu, Bhutia and Lepcha. Bengali was the official language of Colonial Assam for about forty years from the 1830s.

The economy is agrarian. Little land is available for settled agriculture. Along with settled agriculture, jhum (slash-and-burn) cultivation is still practised by a few indigenous groups of people. The inaccessible terrain and internal disturbances has made rapid industrialisation difficult in the region.[citation needed]

In the 21st century, there has been recognition among policy makers and economists of the region that the main stumbling block for economic development of the Northeastern region is the disadvantageous geographical location.[40] It was argued that globalisation propagates deterritorialisation and a borderless world which is often associated with economic integration. With 98 percent of its borders with China, Myanmar, Bhutan, Bangladesh and Nepal, Northeast India appears to have a better scope for development in the era of globalisation.[41] As a result, a new policy developed among intellectuals and politicians that one direction the Northeastern region must be looking to as a new way of development lies with political integration with the rest of India and economic integration with the rest of Asia, with East and Southeast Asia in particular, as the policy of economic integration with the rest of India did not yield much dividends. With the development of this new policy the Government of India directed its Look East policy towards developing the Northeastern region. This policy is reflected in the Year End Review 2004 of the Ministry of External Affairs, which stated that: “India’s Look East Policy has now been given a new dimension by the UPA Government. India is now looking towards a partnership with the ASEAN countries, both within BIMSTEC and the India-ASEAN Summit dialogue as integrally linked to economic and security interests, particularly for India’s East and North East region.”[42]

^"The first group of migrants to settle in this part of the country is perhaps the Austro-Asiatic language speaking people who came here from South-East Asia a few millennia before Christ." (Taher 2001, p. 12)

^"The second group of migrants came to Assam from the north, north-east and east. They are mostly the Tibeto-Burman language speaking people" (Taher 2001, p. 12)

^"From about the fifth century before Christ, there started a trickle of migration of the people speaking Indo-Aryan language from the Gangetic plain." (Taher 2011, p. 12)